The present invention relates to a process for the preparation of N-substituted monochlorosuccinimides.
N-Substituted monochlorosuccinimides are useful as intermediates for the production of resins, medicines and agricultural chemicals and also as precursors of N-substituted maleimides which have recently been utilized as a compound of optical elements.
The conventionally known process for preparing N-substituted monochlorosuccinimide is by ring closure and simultaneous hydrogen chloride addition reaction of a corresponding maleamic acid using an inorganic chlorine compound, such as phosphorus pentachloride and thionyl chloride, or an organic chlorine compound, such as acetyl chloride. For example, a process for preparing N-substituted monochloro-succinimide by reacting maleamic acid with phosphorus pentachloride or thionyl chloride in the absence of a solvent has been described in Journal of General Chemistry of USSR, 26, 211-225 (1956).
In addition, the results of an investigation of the reaction mechanism of maleamic acid with thionyl chloride or acetyl chloride under various reaction conditions have been reported in Journal of Organic Chemistry, 37, 4184-4186(1972).
These conventionally known processes do not provide the desired products in a high yield. Also thionyl chloride evolves toxic sulfur dioxide gas. Phosphorus pentachloride generates phosphorus oxychloride, which is difficult to separate or remove. Consequently, these processes are unsuitable for industrial application.